1. Field of the Invention
Embodiments of the present invention relate generally to semiconductor device manufacturing, and more particularly, to a wafer adapter for use in manufacturing of semiconductor devices.
2. Description of the Related Art
The semiconductor device manufacturing industry has sought continuous increases in wafer size, in order to reduce semiconductor device cost. As is well known, the larger the wafer size is, the more dies can be produced from a single wafer, and thus the lower the cost of an individual die.
However, moving to a larger size wafer typically requires high equipment cost. Furthermore, it is common for semiconductor device manufacturers to produce chips on wafers of two or more different sizes in the same factory. Thus, these factories are required to provide compatibility for wafers of different sizes.
During manufacturing of semiconductor devices, wafers pass through various sophisticated processing steps implemented in different devices to be made into semiconductor dies. In order to simplify transportation and reduce contamination, a Front Opening Unified Pod (FOUP) is usually adopted to transfer wafers from equipment to equipment. Multiple wafers are often accommodated in a FOUP, and the FOUP carrying wafers can be moved to the front of a processing equipment, where wafers are loaded into the processing equipment for processing, and later returned to the FOUP when the process is complete. The FOUP is then transferred to the next processing equipment.
A FOUP is made for accommodating the current largest wafers. A wafer adapter can be used to allow such FOUPs to also carry wafers of smaller size. FIG. 1 schematically illustrates the structure of a conventional FOUP provided with a wafer adapter. As shown in FIG. 1, a wafer adapter 102 capable of carrying wafers of small size is placed in a FOUP 100 suitable for wafers of large size. Wafer adapter 102 is secured in place within FOUP 100 by the force produced by elastic retention wheels 104 against the inner walls of the FOUP.
However, existing elastic retention wheels 104 are prone to crack due to non-uniform force exertion. For example, when elastic retention wheel 104 receives an excessive pressing force, rim 106 of elastic retention wheel 104 may be overly deformed, causing the rim 106 to crack. The cracked edges of elastic retention wheel 104 may easily scratch or even break wafers placed in wafer adapter 102. Also, wafer adapter 102 cannot be stably secured in FOUP 100, which may further cause wafer breakage, contaminating the production or metrology equipment as a result.